The overall aim of this project, in its second renewal, is to improve our understanding of human auditory development, improve the method used to detect hearing loss very early in life and to come to a better understanding of those conditions which lead to early onset hearing loss. This proposal is divided into four main sections. The first section is entitled "Human Auditory Development" and has as its specific aim an improved definition of the tonotopic development of the cochlea, a description of the time course of the development of auditory nonlinearities and a more comprehensive description of the developmental dependencies of various forms of making. The second section of the proposal is entitled "Human Auditory Pathology" and has as its goal the construction of a test battery which can definitively separate middle ear from inner ear from central nervous system auditory pathology, come to an improved understanding of the relationship between abnormalities of masking function and other aspects of auditory capabilities, improve our ability to separate neonatal transient middle ear disorders from more permanent sensory abnormalities, and to determine the presence or absence of nonlinearities as a function of pathologic category. The third section of the proposal is entitled "Animal Models" and it has as its specific aim cross species comparisons of the sequence of maturation using a battery of auditory stimuli to determine the generality of our findings in human infants, to develop a Gunn rat model of ototoxicity and to develop a model of brainstem auditory dysfunction secondary to asphyxia in an acute canine preparation. The final section is entitled "Signal Processing"and has as its specific aims the development of more time efficient algorithms for the collection of responses to transient signals, the development of improved algorithms for obtaining frequency specific information, the development of improved algorithms for defining auditory nonlinearities and to develop a real time microprocessor based implementation of algorithms for the measurement of waveform variability and latency confidence. The successful achievement of these goals will have a significant impact on the clinical practices of pediatric otolaryngology and pediatric audiology in addition to advancing our understanding of the basic mechanisms involved in human auditory development.